1. Field of the Invention
The present invention relates to a nonvolatile memory device and a method of manufacturing the same.
2. Description of the Related Art
In recent years, a resistive random access memory (ReRAM) that stores, in a nonvolatile manner, resistance information, for example, a high resistance state and a low resistance state of an electrically rewritable resistance change element attracts attention as a nonvolatile memory device. In such a ReRAM, for example, variable resistance memory cells in which resistance change elements as storage elements and rectifying elements such as diodes are connected in series are arranged in an array shape in intersections of a plurality of bit lines extending in parallel to a first direction and a plurality of word lines extending in parallel to a second direction perpendicular to the first direction (see, for example, Myoung-Jae Lee; Youngsoo Park; Bo-Soo Kang; Seung-Eon Ahn; Changbum Lee; Kihwan Kim; Wenxu Xianyu; Stefanovich, G.; Jung-Hyun Lee; Seok-Jae Chung; Yeon-Hee Kim; Chang-Soo Lee; Jong-Bong Park; and In-Kyeong Yoo, “2-stack 1D-1R Cross-point Structure with Oxide Diodes as Switch Elements for High Density Resistance RAM Applications,”, IEEE, pp. 771-774, 2007 (Non-Patent Document 1). Examples of the resistance change elements include metal oxides such as NiO, a high resistance state and a low resistance state of which can be switched according to control of a voltage value and voltage application time.
As a memory cell array having structure similar to the ReRAM, a field-programmable ROM having structure in which memory cells of a columnar structure are arranged in an array shape is known. In the memory cells of the columnar structure, diode layers and insulating layers are connected in series in intersections of a plurality of first wires extending in parallel to a first direction and a plurality of second wires extending in parallel to a second direction perpendicular to the first direction (see, for example, S. B. Herner, A. Bandyopadhyay, S. V. Dunton, V. Eckert, J. Gu, K. J. Hsia, S. Hu, C. Jahn, D. Kidwell, M. Konevecki, M. Mahajani, K. Park, C. Petti, S. R. Radigan, U. Raghuram, J. Vienna, M. A. Vyvoda, “Vertical p-i-n polysilicon diode with antifuse for stackable field-programmable ROM”, Electron Device Letters, IEEE, vol. 25, no. 5, pp. 271-273, May 2004 (Non-Patent Document 2)). The field-programmable ROM is manufactured as explained below. First, after a titanium nitride (TiN) film, a p-type polysilicon film, a non-doped polysilicon film are laminated and formed in order on a first wiring layer made of tungsten (W), this laminated film is etched in a columnar shape. Subsequently, spaces in the columnar structure are filled with a silicon oxide film (SiO2 film). The surface of the non-doped polysilicon film is exposed and phosphor (P) is ion-implanted in the surface to form an n-type polysilicon film to thereby form a diode layer of a p-i-n structure. Thereafter, a silicon oxide film is formed in an upper part of the diode layer by a rapid heating and oxidation method. A second wiring layer is formed on the silicon oxide film. Then, the field-programmable ROM is obtained.
However, in the method disclosed in Non-Patent Document 2, when the laminated layer of the titanium nitride film and the polysilicon film is formed in the columnar structure, it is likely that an etching gas and liquid used in the etching come into contact with a side of the laminated layer and deteriorate characteristics of the titanium nitride film and the polysilicon film. Because the silicon oxide film is filled in the spaces in the columnar structure, it is likely that the titanium nitride film and the polysilicon film included in the columnar structure are oxidized. Further, in addition to a lithography process necessary for patterning the lower layer wiring and the upper layer wiring, a lithography process for patterning the laminated layer into the columnar structure is necessary. Therefore, manufacturing cost increases. When the method of manufacturing the field-programmable ROM having such problems is directly applied to the ReRAM, the same problems are likely to be caused.